In the field of oncology, cancer treatment is often performed using radio frequency (RF) ablation techniques. Conventional ablation techniques use an array of RF needles or tines (sometimes referred to as a “tine array”), which may be configured to deploy in a pre-determined shape or pattern for transferring RF energy into surrounding tissue. The needles or tines act as electrodes which are electrically connected to a RF generator. The needles or tines thus transmit RF energy into the surrounding tissue for the thermal coagulation and/or necrosis of tissue. For example, in an undeployed state, tines are positioned at a target area while housed within the lumen of a cannula. The undeployed tine array enclosed within the cannula may be positioned by inserting the cannula through bone and tissue into a target area. Once inserted, the electrode tine array may be deployed by forcing the electrode tines out of a cannula and into the surrounding target tissue. After deployment, RF energy may be transmitted from the electrode tine array to ablate the target tissue, causing heating and eventual necrosis of cancerous or malignant tissue. RF ablation occurs when a high frequency alternating current flows from one electrode to another, completing a current path, causing ionic agitation. Ionic agitation occurs around an active electrode as a result of frictional heating in the tissue surrounding the electrode tines (e.g., electrodes, RF needle probes, and the like) on an array, leading to cell death and necrosis. After ablating the target tissue, the electrode tine array is then retracted into the cannula and the cannula is removed from the target area.
RF ablation probes may be configured in either monopolar or bipolar mode. In monopolar mode, one electrode (e.g., negative) is located within or on a cannula. In order to complete the circuit for RF energy, a separate electrode pad or the like is typically placed on the skin of the patient. Other bipolar-based devices use multiple electrodes or electrode arrays on a single device. For example, the CONCERTO™ needle electrode device (Boston Scientific Scimed, Inc., Maple Grove, Minn.) uses two electrically independent opposing arrays that are contained within an insulated cannula. RF energy passes between the two arrays and heats the tissue surrounding and in between the arrays.
In one known arrangement, the electrode array may be deployed via a distal end of the cannula. Once the electrode array is deployed and activated, RF energy heats the tissue to an elevated temperature so as to ablate and ultimately kill the cancerous tissue. During the ablation process, the pressure inside the tumor (e.g., intra-tumoral pressure) increases due to the heating of moisture within the tissue above its boiling point. Small or localized region(s) within the tumor may include gaseous pockets of heated moisture which leads to a “popping” effect. The popping is caused when the gaseous moisture created within the affected tissue cannot escape readily to the ambient environment and consequently builds up with the tissue until it is liberated in a sudden release. The popping phenomena is of great concern because it is suspected that the popping process may contribute to tumor seeding. For example, cancerous cells may be forcibly expelled or moved during the popping phenomena and become lodged in healthy tissue at which point the cancer may return or spread.
A secondary concern with popping relates to patient comfort. During many percutaneous RF procedures, the subject is consciously sedated during the ablation procedure. The popping of tissue during the application of RF energy to the tissue can be painful to the subject. The popping sound may also be heard by the patient, thereby raising anxiety and discomfort during the procedure.
There thus is a need for a RF ablation device that is able to minimize or eliminate the popping effect that accompanies RF ablation of tissue. Such a device would increase patient comfort as well as reduce the chances of tumor seeding.